Where does all this biomass come from?
Leaf structure and why it matters
Leaves exchange gases via stomata
Active vs Passive stomatal control
Leaf gas exchange impacts global ecology
Vascular tissues in leaves are confined to veins
Transpiration is a by‐product of opening stomatal pores
H2O transport needs to be sufficient to keep stomata open
Venation represents investment in H2O supply
How leaf veins changed the world….
Photosynthesis is complicated….
What do plants do when they are hungry?
Photosynthesis is the basis for most life on Earth
- Greek = “building with light”
- Autotroph = “self nourishing”
- Photoautotroph = “self nourishing with light”
- Photosynthesis is an energy pathway
- 2 linked reactions
- light reaction + Calvin cycle
Chloroplasts: Where the magic happens
The nature of light
When light hits chlorophyll a few things can happen
When pigments absorb photons an election gets excited
Photosystems (2) convert light energy to chemical energy
Light reactions: make ATP + NADPH for Calvin cycle
The Calvin Benson cycle makes sugar
Calvin cycle is a 3-step process
- 1. Fixation: CO2 reacts with 5C molecule (RUBP)
- new 6C split into 2 acids (3C each)
- catalyzed by Rubisco enzyme
- 2. ATP and NADPH turn 3C acids into sugars
- reduction of acids
- 3. Some 3C sugars recycled to make RUBP (5C)
- one 3C sugar leaves to make glucose
- recycling needs ATP
Making sugars requires several cycles
The brillance of photosynthesis
- Light energy to synthesize something…
- is light limiting?
- Carbon dioxide & H2O are everywhere
- easily diffuse into plant
- contain little chemical energy
- non-toxic
- Chemical energy made includes ATP
- high energy
- movable
- recyclable
Calvin Benson won a Nobel prize, his TA won best practical joke
